Re: [PATCH 01/12] tests: add initial bash completion tests

Jeff King [off-list ref] writes:

On Sat, Apr 07, 2012 at 09:25:29PM -0700, Junio C Hamano wrote:

quoted

Bash has a special case code to behave in a "posixly correct" mode, where
a lot of extensions are disabled, when invoked as "sh".  Unfortunately, it
still defines BASH_* variables, including BASH, when operating in this
mode.
[...]
So we may want to be a bit more careful like this:

if test "z${BASH%/bash}" != "z${BASH}"
then
	: ends with bash so we are already running bash as bash

If bash is in posix mode (including "bash --posix" and being invoked as
"bin/sh"), it will set POSIXLY_CORRECT (but not export it). Similarly,
if POSIXLY_CORRECT is set in the outer environment, it will act more
like sh. So maybe that would be a better test.

Yes, but the check needs to be careful to make sure the shell that is
running the check is indeed bash, so that it will explicitly exec bash for
somebody who is running dash but exports POSIXLY_CORRECT to make GNU
programs (other than bash) behave more standard compliant way.

In other words,

	if test -n "$POSIXLY_CORRECT" && test -n "$BASH"
	then
        	: we are running bash under posix mode
	elif ...

or somesuch.